Method and apparatus for inter-radio access network mobility

ABSTRACT

The present disclosure relates to a method and apparatus for optimizing mobility robustness by controlling an inter-Radio Access Technology (inter-RAT) factor. A method for supporting inter-Radio Access Network (RAN) mobility by a source Base Station (BS) in a wireless communication system includes transmitting a handover request message to a target BS, receiving a RAN information request message including a measurement report from the target BS in response to the handover request message, and determining to amend a mobility setting, if it is determined that an unnecessary handover has occurred based on the RAN information request message. The handover request message includes at least one of a Tracking Area Identifier (TAI) of a tracking area to which the source BS belongs, a global BS Identifier (ID), and an E-UTRAN (Evolved-UMTS (Universal Mobile Telecommunication System) Terrestrial Radio Access Network) Cell Global ID (ECGI).

PRIORITY

This application is a continuation application of prior application Ser. No. 14/707,597, filed on May 8, 2015, which claimed priority under 35 U.S.C. § 119(a) to a Korean Patent Application filed in the Korean Intellectual Property Office on May 8, 2014 and assigned Serial No. 10-2014-0054815, the entire disclosure of each of which is incorporated herein by reference.

BACKGROUND OF THE DISCLOSURE 1. Field of the Disclosure

The present disclosure relates to a method and apparatus for supporting mobility by controlling a mobility factor in a wireless communication system.

2. Description of the Related Art

To meet the demand for wireless data traffic having increased since deployment of 4G (4th-Generation) communication systems, efforts have been made to develop an improved 5G (5th-Generation) or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called a ‘Beyond 4G Network’ or a ‘Post LTE System’. The 5G communication system is considered to be implemented in higher frequency (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higher data rates. To decrease propagation loss of the radio waves and increase the transmission distance, the beamforming, massive multiple-input multiple-output (MIMO), Full Dimensional MIMO (FD-MIMO), array antenna, an analog beam forming, large scale antenna techniques are discussed in 5G communication systems. In addition, in 5G communication systems, development for system network improvement is under way based on advanced small cells, cloud Radio Access Networks (RANs), ultra-dense networks, device-to-device (D2D) communication, wireless backhaul, moving network, cooperative communication, Coordinated Multi-Points (CoMP), reception-end interference cancellation and the like. In the 5G system, Hybrid FSK and QAM Modulation (FQAM) and sliding window superposition coding (SWSC) as an advanced coding modulation (ACM), and filter bank multi carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) as an advanced access technology have been developed.

The Internet, which is a human centered connectivity network where humans generate and consume information, is now evolving to the Internet of Things (IoT) where distributed entities, such as things, exchange and process information without human intervention. The Internet of Everything (IoE), which is a combination of the IoT technology and the Big Data processing technology through connection with a cloud server, has emerged. As technology elements, such as “sensing technology”, “wired/wireless communication and network infrastructure”, “service interface technology”, and “Security technology” have been demanded for IoT implementation, a sensor network, a Machine-to-Machine (M2M) communication, Machine Type Communication (MTC), and so forth have been recently researched. Such an IoT environment may provide intelligent Internet technology services that create a new value to human life by collecting and analyzing data generated among connected things. IoT may be applied to a variety of fields including smart home, smart building, smart city, smart car or connected cars, smart grid, health care, smart appliances and advanced medical services through convergence and combination between existing Information Technology (IT) and various industrial applications.

In line with this, various attempts have been made to apply 5G communication systems to IoT networks. For example, technologies such as a sensor network, Machine Type Communication (MTC), and Machine-to-Machine (M2M) communication may be implemented by beamforming, MIMO, and array antennas. Application of a cloud Radio Access Network (RAN) as the above-described Big Data processing technology may also be considered to be as an example of convergence between the 5G technology and the IoT technology.

Wireless communication systems were first developed to provide voice service, while ensuring the mobility of users. The wireless communication systems have been extended to data service beyond voice service. At present, the wireless communication systems provide high-rate data service.

Such a wireless communication system may include at least one Radio Access Network (RAN) and a Core Network (CN). Because each RAN covers a different area, a handover between different RANs may be required. For example, a relatively early developed Enhanced Data rates for GSM Evolution (EDGE) RAN (GERAN, called a 2^(nd) Generation (2G) network) may have been deployed across a broad area, whereas a relatively recently developed Evolved-UMTS (Universal Mobile Telecommunication System) Terrestrial Radio Access Network (E-UTRAN, called a Long Term Evolution (LTE) network) may have been deployed over smaller areas. In this case, if a User Equipment (UE) moves out of the coverage of the LTE network during reception of a service from the LTE network, the UE may receive the service from the GERAN. Thus, a handover from the LTE network to the GERAN occurs.

A source Radio Access Point (RAP) determines a handover. Many handover decision methods are available. One of the handover decision methods is that an RAP compares a measurement received from a UE with an internal threshold and if a predetermined condition is satisfied, the RAP determines to perform a handover.

Unless an appropriate mobility setting is performed in a handover-related RAP, an abnormal handover (for example, an untimely handover or an unnecessary handover) may occur. Accordingly, there is a need for effectively performing a mobility setting in a handover-related RAP in a wireless communication system.

SUMMARY

An aspect of the present disclosure is to provide a method and apparatus for supporting inter-Radio Access Technology (RAT) mobility in a wireless communication system.

Another aspect of the present disclosure is to provide a method and apparatus for sensing occurrence of an abnormal handover and supporting mobility using mobility setting information in a wireless communication system.

In accordance with an aspect of the present disclosure, there is provided a method for supporting inter-Radio Access Network (RAN) mobility by a source Base Station (BS) in a wireless communication system. The method includes transmitting a handover request message to a target BS, receiving a RAN information request message including a measurement report from the target BS in response to the handover request message, and determining to amend a mobility setting, if it is determined that an unnecessary handover has occurred based on the RAN information request message. The handover request message includes at least one of a Tracking Area Identifier (TAI) of a tracking area to which the source BS belongs, a global BS Identifier (ID), and an E-UTRAN (Evolved-UMTS (Universal Mobile Telecommunication System) Terrestrial Radio Access Network) Cell Global ID (ECGI).

In accordance with another aspect of the present disclosure, there is provided a method for supporting inter-RAN mobility by a target BS in a wireless communication system. The method includes receiving a handover request message from a source BS, and transmitting to the source BS a RAN information request message including a measurement and indicating occurrence of an unnecessary handover in response to the handover request message. The handover request message includes at least one of a TAI of a tracking area to which the source BS belongs, a global BS ID, and an ECGI.

In accordance with another aspect of the present disclosure, there is provided an apparatus of a source BS for supporting inter-RAN mobility in a wireless communication system. The apparatus includes a transceiver for transmitting a handover request message to a target BS, and receiving a RAN information request message including a measurement report from the target BS in response to the handover request message, and a controller for determining to amend a mobility setting, if it is determined that an unnecessary handover has occurred based on the RAN information request message. The handover request message includes at least one of a TAI of a tracking area to which the source BS belongs, a global BS ID, and an ECGI.

In accordance with another aspect of the present disclosure, there is provided an apparatus of a target BS for supporting inter-RAN mobility in a wireless communication system. The apparatus includes a transceiver for receiving a handover request message from a source BS, and transmitting a RAN information request message to the source BS, and a controller for generating the RAN information request message including a measurement and indicating occurrence of an unnecessary handover in response to the handover request message. The handover request message includes at least one of a TAI of a tracking area to which the source BS belongs, a global BS ID, and an ECGI.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and advantages of certain exemplary embodiments of the present disclosure will be more apparent from the following description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a diagram illustrating a configuration of a wireless communication system to which the present disclosure is applied;

FIG. 2 is a block diagram illustrating each device included in the wireless communication system according to an embodiment of the present disclosure;

FIG. 3 is a diagram illustrating a signal flow for an operation for sensing an unnecessary inter-Radio Access Network (inter-RAN) handover according to a first embodiment of the present disclosure;

FIG. 4 is a diagram illustrating a signal flow for an operation for sensing an unnecessary inter-RAN handover according to a second embodiment of the present disclosure;

FIG. 5 is a flowchart illustrating an operation of a Radio Access Point (RAP) when the RAP receives an HO Report message according to an embodiment of the present disclosure;

FIG. 6 is a diagram illustrating a signal flow for an operation for adjusting a mobility setting by sensing an unnecessary handover at a source RAP 110 a according to a third embodiment of the present disclosure; and

FIG. 7 is a diagram illustrating a signal flow for an operation for adjusting a mobility setting by sensing an unnecessary handover using a trace function at the source RAP 110 a according to an embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

With reference to the attached drawings, preferred embodiments of the present disclosure will be described in detail. Like reference numerals denote the same components in the drawings. Known functions and configurations will not be described in detail lest they should obscure the subject matter of the present disclosure.

While the following detailed description is given of embodiments of the present disclosure mainly in the context of a Long Term Evolution (LTE) network and an Evolved Packet Core (EPC) as a Radio Access Network (RAN) and a Core Network (CN), respectively, which are defined by the 3^(rd) Generation Partnership Project (3GPP), those skilled in the art will understand that a slight modification can be made to the subject matter of the present disclosure in other communication systems having similar technological backgrounds without departing the scope and spirit of the present disclosure.

FIG. 1 is a diagram illustrating a configuration of a wireless communication system to which the present disclosure is applied.

Referring to FIG. 1, the wireless communication system may include a User Equipment (UE) 100, one or more RANs 113 a and 113 b, and a CN 130. In the example of FIG. 1, two RANs 113 a and 113 b exist.

The RANs 113 a and 113 b are classified depending on their Radio Access Technologies (RATs). Therefore, the terms RAN and RAT are interchangeably used. Major examples of the RANs 113 a and 113 b include an Enhanced Data rates for GSM Evolution (EDGE) RAN (GERAN), an Evolved-UMTS (Universal Mobile Telecommunication System) Terrestrial Radio Access Network (E-UTRAN, called a 3G network), and an LTE network. Aside from exceptions, the UE 100 may usually establish a connection only with one RAN, for data and/or signaling communication.

Each of the RANs 113 a and 113 b may include a few components. While each of the RANs 113 a and 113 b is shown in FIG. 1 as having a single component, for simplicity, it may include a plurality of components. Among the components of the RANs 113 a and 113 b, RAN components 110 a and 110 b interacting with the UE 100 may communicate with the UE 100 via radio interfaces 105 a and 105 b, respectively. The other components of the wireless communication system may be connected mainly wiredly. Each of the RAN components 110 a and 110 b interacting with the UE 100 may be one of, for example, an evolved Node B (eNB), a Node B (NB), and/or a Radio Network Subsystem (RNS) including an eNB or an NB, a Base Transceiver Station (BTS) or a Base Station Subsystem (BSS) including a BTS, a wireless access point, a home eNB, a home NB, a home eNB GateWay (GW), and an X2 GW. For the convenience of description, the term “RAP” is used to signify at least one of the above examples of the RAN components 110 a and 110 b or a RAN itself.

Each of the RAPs 110 a and 110 b may include one or more cells. A cell covers a specific area and the UE 100 is serviced within the coverage of a cell. Herein, the cell is equivalent to a cell of a cellular system and the RAPs 110 a and 110 b are devices that manage and control the cells. However, the RAPs 110 a and 110 b and the cells may be used in the same meaning, for the convenience of description in the present disclosure. When an object (for example, an embodiment) is described, the terms cell and RAP may be interchangeably used, for the convenience of description.

The CN 130 may include RAN control elements 120 a and 120 b. The RAN control elements 120 a and 120 b are responsible for overall control functionalities including mobility management, authentication, and security. Each of the RAN control elements 120 a and 120 b may be at least one of, for example, a Mobility Management Entity (MME), a Serving GPRS (General Packet Radio Service) Support Node (SGSN), and a Mobile Switching Center (MSC).

The different RAN control elements 120 a and 120 b may be connected to the RAPs 110 a and 110 b of the different RANs 113 a and 113 b. For example,

the eNB 110 a of the E-UTRAN 113 a may be connected to the MME 120 a; and

the RNS 110 b of the UTRAN 113 b may be connected to the SGSN 120 b and/or the MSC 120 b;

the BSS 110 a of the GERAN 113 a may be connected to the SGSN 120 a and/or the MSC 120 a.

In the presence of information to be transmitted between the RAPs 110 a and 110 b belonging to the different RANs 113 a and 113 b, the information is transmitted generally through the RAN control element 120 a because there is no interface defined between the RAPs 110 a and 110 b. For example, if the RAP 110 a has information to be transmitted to the other RAP 110 b, the information may be transmitted through an interface 115 a defined between the RAP 110 a and the RAN control element 120 a, an interface 123 defined between the RAN control element 120 a and the other RAN control element 120 b, and an interface 115 b defined between the RAN control element 120 b and the RAP 110 b.

[Table 1] and [Table 2] below list the names of the interfaces 115 a and 115 b and the interface 123 according to the types of terminal ends.

TABLE 1 RAN control element-RAP Names of the interfaces 115a and 115b MME-eNB S1-MME SGSN-RNS Iu-PS MSC-RNS Iu-CS SGSN-BSS Gb or Iu-PS MSC-BSS A or Iu-CS

TABLE 2 RAN control element-RAN control element Name of interface 123 MME-MME S10 MME-SGSN S3 MME-MSC SGs or Sv SGSN-SGSN Gn or S16 SGSN-MSC Gs or Sv MSC-MSC E

Because the different RANs 113 a and 113 b cover different areas, a handover between the RANs 113 a and 113 b is required. The source RAP 110 a or 110 b determines the handover. One of many available handover decision methods is that an RAP compares a measurement received from the UE 100 with its internal threshold and then, if a predetermined condition is satisfied, the RAP determines to perform a handover.

Now, a description will be given of an apparatus and method for sensing an abnormal handover, when the source RAP 110 a or 110 b determines a handover.

FIG. 2 is a block diagram illustrating each device included in the wireless communication system according to an embodiment of the present disclosure.

Each device included in the wireless communication system illustrated in FIG. 1 includes a controller 210, a transmitter 231, and a receiver 233. The transmitter 231 and the receiver 233 may be incorporated into a single unit.

The controller 210 controls operations of the device according to an embodiment of the present disclosure. Particularly, the controller 210 generates a message for a handover in the device and controls the transmitter 231 to transmit the message to another device. The transmitter 231 transmits the message and the receiver 233 receives a message from another device, under the control of the controller 210.

FIG. 3 is a diagram illustrating a signal flow for an operation for sensing an unnecessary inter-RAN handover according to a first embodiment of the present disclosure.

According to the first embodiment of the present disclosure, when a handover occurs between the different RANs 113 a and 113 b, the RAP 110 a transmits routing information about the RAN 113 a to the RAP 110 b of the RAN 113 b so that if the RAP 110 b senses a specific condition, the RAP 110 b may transmit corresponding information to the RAP 110 a of the RAN 113 a. Herein, the RAP 110 a is referred to as a source RAP 110 a, the RAP 110 b is referred to as a target RAP 110 b, the RAN 113 a including the source RAP 110 a is referred to as a source RAN 113 a, and the RAN 113 b including the target RAP 110 b is referred to as a target RAN 113 b.

Referring to FIG. 3, the UE 100 may receive user data (that is, a service) from the source RAP 110 a in step 300. In the first embodiment of the present disclosure, when it is said that the UE 100 receives a service from the RAPs 110 a and 110 b, this means that there are a context for the UE 100 in the RAPs 110 a and 110 b and the UE 100 exchanges user data and signaling with the RAPs 110 a and 110 b.

If the source RAP 110 a determines that it is appropriate for the UE 100 to receive a service from the target RAN 113 b, more specifically to receive user data from the target RAP 110 b of the target RAN 113 b, the source RAP 110 a determines a handover of the UE 100 to the target RAN 113 b in step 305.

In step 310, the source RAP 110 a transmits a message requesting preparation for a handover to the RAN control element 120 a. The message requesting preparation for a handover may be a Handover Required message. The Handover Required message may include a transparent container transmitted to the target RAP 110 b transparently (the intermediate RAN control elements 120 a and 120 b do not need to interpret or are not supposed to interpret the transparent container). The transparent container included in the Handover Required message may include at least one of routing information about the source RAP 110 a, a measurement quantity related to the source RAN 113 a, a reporting threshold used in analyzing the measurement result of the measurement quantity, a duration over which the target RAP 110 b should collect a measurement result from the UE 100 after a successful inter-RAN handover, and a measurement frequency bandwidth.

The routing information about the source RAP 110 a may include at least one of a Tracking Area Identity (TAI), a global eNB ID, and an E-UTRAN Cell Global Identity (ECGI). Upon receipt of both the global eNB ID and the ECGI, the target RAP 110 b is naturally aware of the TAI, global eNB ID, and ECGI of the source RAP 110 a.

Aside from the above scheme, a more efficient transmission scheme for indicating the global eNB ID and ECGI of the source RAP 110 a to the target RAP 110 b may be contemplated, based on the idea that the ECGI and global eNB ID of a home eNB are identical and the global eNB ID of any other eNB is a part of its ECGI.

-   -   The source RAP 110 a transmits only the ECGI without the global         eNB ID. In addition, the source RAP 110 a transmits an indicator         indicating whether it is a home eNB or not (the indicator may         indicate whether the source RAP 110 a is a home eNB, may be         transmitted only when the source RAP 110 a is a home eNB, may         indicate whether the source RAP 110 a is a general eNB, or may         be transmitted only when the source RAP 110 a is a general eNB).         If the source RAP 110 a is not a home eNB, the target RAP 110 b         extracts the global eNB ID from the ECGI (by removing the last         eight bits of the ECGI). If the source RAP 110 a is a home eNB,         the target RAP 110 b sets the global eNB ID to the ECGI.     -   If the source RAP 110 a is a home eNB, the source RAP 110 a         transmits only the ECGI without the global eNB ID. Otherwise,         the source RAP 110 a transmits both the global eNB ID and the         ECGI. Upon receipt of the ECGI only, the target RAP 110 b         extracts the global eNB ID from the ECGI (by removing the last         eight bits of the ECGI). If the source RAP 110 a is a home eNB,         the target RAP 110 b does not need to extract the global eNB ID.     -   The source RAP 110 a transmits only the ECGI. The target RAP 110         b determines whether the source RAP 110 a is a home eNB using         configuration information preserved in the target RAP 110 b. If         the source RAP 110 a is not a home eNB, the target RAP 110 b         extracts the global eNB ID from the ECGI (by removing the last         eight bits of the ECGI). If the source RAP 110 a is a home eNB,         the target RAP 110 b sets the global eNB ID to the ECGI.

An operation to be performed when the target RAP 110 b is aware of the TAI, global eNB ID, and ECGI of the source RAP 110 a in the above-described method will be described in detail with reference to step 340.

At least one of the above-described TAI, global eNB ID, ECGI, and indicator indicating whether the RAP 110 a is a home eNB may be transmitted in a transparent container (a source BSS to target BSS transparent container and/or old BSS to new BSS information) in many manners:

-   -   transmitted in an IRAT Measurement Configuration Information         Element (IE) of the transparent container; and     -   transmitted in a separate (new) IE (for example, a UE History         Information IE) other than the IRAT Measurement Configuration IE         in the transparent container.

[Table 3] below illustrates an exemplary configuration of the IRAT Measurement Configuration IE, when all of the TAI, the global eNB ID, and the ECG are transmitted in the IRAT Measurement Configuration IE of the transparent container. The TAI, the global eNB ID, and the ECG may be arranged appropriately, in consideration of a TAI length of 40 bits, a global eNB ID length of 20 bits for a general eNB and 28 bits for a home eNB, and an ECGI length of 28 bits.

TABLE 3 8 7 6 5 4 3 2 1 Octet 1 IEI Octet 2 Length Indicator Octet 3 pare REP_QUANT REPORTING_THRESH- OLD Octet 4 Measurement_Duration Octets 5-6 E-ARFCN Octet 7 Spare Measure- ment Bandwidth Octets 8-9 E-ARFCN Octet 10 Spare Measure- ment Bandwidth ″ ″ Measure- ment Bandwidth Octets m-(m + 1) E-ARFCN Octet m + 2 Spare Measure- ment Bandwidth Octets m + 3-m + 7 Octets 4 to 8 contain the value part (starting with octet 2) of the Tracking Area Identity IE defined in 3GPP TS 24.301 [37], not including 3GPP TS 24.301 IEI [37] Octets m + 8-n Global eNB ID Octets n + 1-n + 7 E-UTRAN CGI

The RAN control element 120 a transmits a message to the RAN control element 120 b of the target RAN 113 b in step 315. The message may be a Forward Relocation Request message. The Forward Relocation Request message may include at least one of a transparent container and routing information about the source RAP 110 a. Once the RAN control element 120 a transmits the routing information about the source RAP 110 a, the routing information about the source RAP 110 a may be transmitted to the target RAP 113 b even though the transparent container does not include the routing information about the source RAP 110 a in step 310. As described before, the RAN control element 120 preserves the routing information about the RAP 110 of the UE 100 because the RAN control element 120 is responsible for overall control of the mobility of the UE 100.

The RAN control element 120 b may transmit a Hanover Required message to the target RAP 110 b in step 320. The Handover Required message may be a PS-HANDOVER-REQUEST message or a Handover Request message. The Hanover Required message may include at least one of a transparent container (a source BSS to target BSS transparent container and/or old BSS to new BSS information) and the routing information about the source RAP 110 a.

The routing information about the source RAP 110 a may be transmitted without using a transparent container in steps 315 and 320 in at least one of the methods for determining the global eNB ID and ECGI of the source RAP 110 a by the target RAP 110 b, described before with reference to step 310. The TAI may be apparently transmitted. The method for transmitting the routing information about the source RAP 110 a in a transparent container as described in step 310 is different, just in terms of a transmission medium, from the method for transmitting the routing information about the source RAP 110 a in IEs of the two messages transmitted in steps 315 and 320, not in a transparent container. It is to be clearly understood that the method for more efficiently indicating the global eNB ID and ECGI of the source RAP 110 a to the target RAP 110 b is applicable to the method for transmitting the routing information about the source RAP 110 a in IEs of the two messages transmitted in steps 315 and 320, not in a transparent container.

The remaining handover procedure may be performed in step 325. Then, the UE 100 may receive a service from the target RAP 110 b in step 330. During the handover, the UE 100 may transmit routing information about the source RAN 110 a. The routing information about the source RAN 110 a may be transmitted in a Handover Access message. The routing information about the source RAN 110 a may be carried in a Handover Reference Information IE of the message. The Handover Reference Information IE may not carry the TAI, the ECGI, and/or the global eNB ID due to its limited size. In this case, the UE 100 may indicate the source RAP 110 a using a Physical Cell Identifier (PCI, the PCI is shorter) of a cell within the source RAP 110 a, and the RAP 110 b may acquire the routing information about the source RAP 110 a using configuration information preserved in the RAP 110 b.

Referring to FIG. 3 again, the target RAP 110 b may instruct the UE 100 to continuously measure about the source RAN 113 a, based on the received information in step 335. The measurement target may be determined based on at least one of the measurement quantity related to the RAN 113 a and the measurement frequency/bandwidth received in the transparent container. The UE 100 may perform a measurement as instructed by the target RAP 110 b and transmit a report of the measurement to the target RAP 110 b periodically or intermittently in step 338.

Upon expiration of the duration set in the transparent container, the target RAP 110 b may determine whether all measurement results of one or more cells within a predetermined time exceed a threshold by comparing the measurement report received from the UE 100 with the threshold received in the transparent container. If all measurement results of at least one cell exceed the threshold, this may imply that the UE 100 has performed an unnecessary handover to the target RAP 113 b even though the UE 100 may receive a service sufficiently from a cell of the source RAN 113. Upon sensing the unnecessary inter-RAN handover, the target RAP 110 b may determine to indicate the unnecessary handover to the source RAN 113 a in step 340.

The target RAP 110 b transmits a message carrying RAN Information Management (RIM) information to the source RAP 110 a through the RAN control elements 120 a and 120 b in steps 345, 347, and 349. The message carrying the RIM information may be a RAN Information Request message. The RAN Information Request message may include a RIM container and, in addition, routing information about a destination of the RIM container.

The RIM container may include information (an HO Report) helpful for the source RAP 110 a to recognize and solve the problem (i.e., the unnecessary handover). The information (the HO Report) may include at least one of an HO type indicating LTE to UTRAN or LTE to GERAN, an HO report type indicating report of an unnecessary handover to another RAN, an HO source ID (a cell ID within the RAP 110 a), an HO target ID (a cell ID within the RAP 110 b), and a candidate cell list (listing cells having all measurement results exceeding a threshold during a time period). Among them, the HO source ID may indicate the ECGI of a source cell in the source RAP 110 a. The destination of the RIM container may be the source RAP 110 a. Routing information about the RIM container destination may include at least one of a TAI and a global eNB ID. Accordingly, the target RAP 110 b may need the TAI, global eNB ID, and ECGI of the source RAP 110 a. The target RAP 110 b may determine the TAI, global eNB, and ECGI of the source RAP 110 a by at least one of

-   -   the method for transmitting the routing information about the         source RAP 110 a in a transparent container, described before in         relation to step 310; and     -   the method for transmitting the routing information about the         source RAP 110 a by a PS-Handover-Request message and a Handover         Request message, described before in relation to step 321, may         fill the HO source ID based on the determined ECGI, and may fill         the routing information about the RIM container destination         based on the determined TAI and global eNB ID.

The RIM container may be transmitted to the source RAP 110 a through the RAN control elements 120 b and 120 a in steps 347 and 349. The RAN control element 120 b may select the RAN control element 120 a using the routing information about the RIM container destination received from the RAP 110 b, that is, the TAI and/or the global eNB ID. Further, the RAN control element 120 a may receive the TAI and/or the global eNB ID from the RAN control element 120 b, detect the appropriate RAP 110 a, and transmit the RIM container to the RAP 110 a.

Upon receipt of the RIM container, the source RAP 110 a may amend a mobility setting, determining that an unnecessary handover has occurred in step 350.

The source RAP 110 a transmits RAN information to the target RAP 110 b through the RAN control elements 120 a and 120 b in response to the RIM container in step 355. The target RAP 110 b transmits a RAN information ACKnowledgment (ACK) message to the source RAP 110 a through the RAN control elements 120 a and 120 b in step 360.

It is to be clearly understood that the method for transmitting routing information according to the embodiment of the present disclosure is not necessarily for sensing an unnecessary handover but may be modified partially or wholly whenever there is a need for transmitting routing information.

FIG. 4 is a diagram illustrating a signal flow for an operation for sensing an unnecessary inter-RAN handover according to a second embodiment of the present disclosure.

According to the second embodiment of the present disclosure, even though the source RAP 110 a does not transmit routing information about the source RAP 110 a to the target RAP 110 b, the target RAP 110 b may infer the routing information about the source RAP 110 a based on an initial measurement result after a handover from the source RAP 110 a to the target RAP 110 b.

The handover from the source RAP 110 a to the target RAP 110 b may be performed successfully in step 430. The second embodiment of the present disclosure may correspond to all or part of steps 300 to 330 in the first embodiment of the present disclosure.

The target RAP 110 b transmits measurement information instructing a measurement to the UE 100 in step 435 and the UE 100 transmits a measurement report to the target RAP 110 b in step 438. The target RAP 110 b may receive one or more measurement reports during a time period indicated in step 430 and may recognize occurrence of an unnecessary handover based on the measurement report.

Upon sensing occurrence of the unnecessary handover, the target RAP 110 b determines to notify the source RAP 110 a of the unnecessary handover in step 440. The unnecessary handover may be notified to the source RAP 110 a in messages transmitted in steps 445, 447, and 449. The message transmitted in step 445 may include a RIM container and/or routing information about a RIM container destination. The RIM container may need to include the ECGI of a source cell within the RAP 110 a, and the routing information about the RIM container destination may include the TAI and global eNB ID of the source RAP 110 a.

The target RAP 110 b may infer at least one of the TAI, global eNB ID, and ECGI of the source RAP 110 a using a measurement report received from the UE 100 and/or configuration information preserved in the RAP 110 b. For example, the target RAP 110 b may identify a cell having a largest signal strength from an initial measurement report received after the handover, infer at least one of the TAI, the global eNB ID, and the ECGI of the source RAP 110 a using configuration information about the identified cell, and perform the next step, assuming that the inferred information is information about a source cell within the source RAP 110 a.

A more simple method for determining a source cell is to depend only on the configuration information preserved in the RAP 110 b. If the RAP 110 a is unusually deployed around the RAP 110 b, the source cell may be accurately determined just using the configuration information. In another example, an adjacent cell of the RAN 113 a may be selected randomly and determined to be the source cell. The source cell may be determined using two or more of the above-described determination methods in combination.

The target RAP 110 b may fill a part of the RIM container and the routing information about the RIM container destination using the inferred at least one of the TAI, the global eNB ID, and the ECGI in step 445. Step 445 and the subsequent steps may be performed similarly to step 345 and the subsequent steps in the first embodiment of the present disclosure and thus will not be described herein in detail.

FIG. 5 is a flowchart illustrating an operation of a RAP when the RAP receives an HO Report message according to an embodiment of the present disclosure.

According to the embodiment of the present disclosure, even though a HO Report is transmitted to a RAP other than the RAP 110 a including a cell (a source cell of an unnecessary handover) that is supposed to receive the HO Report, the HO Report may be verified. If the HO Report is not valid, the HO Report may be ignored, thereby preventing unnecessary adjustment of a mobility setting.

If routing information about a source cell within the source RAP 110 a is transmitted as in the first embodiment, the HO Report may be transmitted to the right RAP 110 a, that is, the RAP 110 a that has incurred the unnecessary handover. On the other hand, if the routing information about the source cell within the source RAP 110 a is not transmitted and the source RAP 110 a is inferred as in the second embodiment, the HO Report may be transmitted to a RAP other than the RAP 110 a that has incurred the unnecessary handover. If the HO Report is transmitted to the wrong RAP and manipulates a well-set mobility setting of the RAP 110, network performance may be adversely affected. Therefore, the RAP receiving the HO Report may need a procedure as illustrated in FIG. 5 to verify the HO Report.

Referring to FIG. 5, a RAP receives an HO Report in step 500. The RAP verifies the HO Report in step 510. The HOR Report may be verified in various manners depending on implementation. For example, there may be a value frequently set as a duration included in a transparent container of a Handover Required message, for each RAP. Upon receipt of a HO Report, a RAP determines whether it has performed a handover to a HO target ID set in the HO Report before a time corresponding to the value frequently set in the duration (+margin). If the RAP has performed a handover, the RAP may determine that the HO Report is valid and otherwise, the RAP may determine that the HO Report is not valid. The margin may be set in consideration of a transmission delay and a processing delay. In another example, when the target RAP 110 b transmits a HO Report, it may include the whole or part of the contents of an IRAT Measurement Configuration received from the source RAP 110 a during the handover. Upon receipt of the HO Report including the whole or part of the contents of the IRAT Measurement Configuration, the RAP determines whether the received IRAT Measurement Configuration is an IRAT Measurement Configuration frequently set by the RAP. If the IRAT Measurement Configurations are identical, the RAP may determine that the HO Report is valid and otherwise, the RAP may determine that the HO Report is not valid.

If the RAP determines that the HO Report is valid, the RAP processes the HO Report in step 520. For example, if the RAP has received HO Reports that may be classified into the same HO Report a predetermined number of or more times or as often as or more often than a predetermined time interval, the RAP may reflect the HO Reports in a mobility setting.

If the RAP determines that the HO Report is not valid, the RAP ignores the HO Report in step 530.

Now, a description will be given of third and fourth embodiments for sensing an unnecessary handover and thus adjusting a mobility setting by the source RAP 110 a with reference to FIGS. 6 and 7.

FIG. 6 is a diagram illustrating a signal flow for an operation for adjusting a mobility setting by sensing an unnecessary handover at the source RAP 110 a according to a third embodiment of the present disclosure.

According to the third embodiment of the present disclosure, an Operation, Administration, and Maintenance (OAM) may monitor the RAP 110 b continuously. If the RAP 110 b transmits a HO Report more frequently, and/or if the number of transmissions of a HO Report exceeds a predetermined number, the OAM may detect the RAP 110 a and induce the RAP 110 a to amend a mobility setting.

Once the target RAP 110 b senses an unnecessary handover and determines to notify the source RAP 110 a of the unnecessary handover, the target RAP 110 b may transmit a message to the RAN control element 120 b by containing a HO Report in a RIM container in step 645. An OAM 600 continuously monitors RAPs in step 660. If the OAM 600 senses the message frequently or a predetermined number of or more times, the OAM 600 detects the problematic RAP 110 a and induces the RAP 110 a to amend a mobility setting, determining that there is a problem with the mobility setting of the RAP 110 a in step 670.

FIG. 7 is a diagram illustrating a signal flow for an operation for adjusting a mobility setting by sensing an unnecessary handover using a trace function at the source RAP 110 a according to a fourth embodiment of the present disclosure.

According to the embodiment of the present disclosure, a Trace Collection Entity (TCE) 710 may sense an unnecessary handover and induce amendment in a mobility setting.

An Element Manager (EM) 700 may configure the source RAP 110 a and/or the target RAP 110 b to report a specific event, upon occurrence of the specific event in steps 720 and 723. For example, the source RAP 110 a may be configured to report transmission of an IRAT Measurement Configuration IE to the TCE (through another entity), when it transmits the IRAT Measurement Configuration IE (to speak more generally, when it transmits additional information for sensing an unnecessary handover), and the target RAP 110 b may be configured to report transmission of a HO Report to the TCE (through another entity), when it transmits the HO Report. The EM 700 may transmit information about the configurations to the RAPs 110 a and 110 b, not directly but through a few other entities.

When a Handover Required message including an IRAT Measurement Configuration IE is transmitted in step 725 or when a RAN Information Request message including a HO Report is transmitted in step 730, information about the event may be transmitted to the TCE 710 in steps 735/750 and 740/745).

In the absence of detailed information (for example, an IMSI) about the UE in the RAP 110 a, the RAP 110 a may transmit report information about the event to the TCE 710 through the RAN control element 120 a in steps 735 and 750. At least one of a message transmitted from the RAP 110 a to the RAN control element 120 a and a message transmitted from the RAN control element 120 a to the TCE 710 may include a part of a IRATMeasurement Configuration IE or a IRATMeasurement Configuration IE.

In the presence of the detailed information (for example, the IMSI) about the UE in the RAP 110 b, the RAP 110 b may exchange information with the RAN control element 120 b, for acquisition of additional information (for example, an IMEI(SV)) in step 740, or may transmit report information about the event directly to the TCE 710 without the information exchange in step 745. Herein, the information transmitted from the RAP 110 b to the TCE 710 may include a HO Report or its part.

The TCE 710, which has collected the information, may sense occurrence of an unnecessary handover in conjunction with the OAM 600 in step 755. Upon sensing an unnecessary handover, the TCE 710 determines that there is a problem with a mobility setting of the RAP 110 a, detects the RAP 110 a, and induces the RAP 110 a to amend the mobility setting in step 760.

In the foregoing embodiments, any of the steps and messages may be selective or omitted. In each embodiment, the steps may not be performed always in a predetermined order and thus their sequence may be changed. Messages may not be transmitted always in a predetermined order and thus their delivery sequence may be changed. Each step and each message may be implemented independently.

The whole or a part of the tables given as examples in the foregoing embodiments is presented to help the understanding of the present disclosure. Therefore, details of the tables may be considered to be a representation of a part of the method and apparatus proposed by the present disclosure. In other words, a semantic approach may be preferred to a communicative approach to the contents of the tables.

While the disclosure has been shown and described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the disclosure as defined by the appended claims and their equivalents. 

What is claimed is:
 1. A method of a first base station in a wireless communication system, the method comprising: transmitting, by the first base station to a second base station, a message requesting an inter-radio access technology (RAT) handover from a cell of the first base station to a cell of the second base station, the message including inter-RAT measurement configuration information, a tracking area identity (TAI), an identifier of the first base station, and an identifier of the cell of the first base station; and receiving, by the first base station from the second base station, a handover report indicating that the inter-RAT handover is unnecessary after the inter-RAT handover to the second base station is performed successfully, the handover report including the identifier of the cell of the first base station, wherein the inter-RAT measurement configuration information includes information on a duration in which the second base station is to collect measurement results and information on a frequency for which the second base station collects the measurement results, and wherein the measurement results are received from the UE by instructing the UE to measure the frequency.
 2. The method of claim 1, wherein the handover report further includes at least one of a handover type, a handover report type, a handover target ID, or a candidate cell list.
 3. The method of claim 1, wherein the identifier of the cell of the first base station includes an evolved-universal mobile telecommunication system terrestrial radio access network (E-UTRAN) cell global identifier (ECGI).
 4. The method of claim 1, wherein it is determined that the handover is unnecessary when the duration expires.
 5. A method of a second base station in a wireless communication system, the method comprising: receiving, from a first base station, a message requesting an inter-radio access technology (RAT) handover from a cell of the first base station to a cell of the second base station, the message including inter-RAT measurement configuration information, a tracking area identity (TAI), an identifier of the first base station, and an identifier of the cell of the first base station, the inter-RAT measurement configuration information includes information on a duration in which the second base station is to collect measurement results and information on a frequency for which the second base station collects the measurement results; receiving measurements results of the frequency for the duration of collecting the measurements results by instructing the UE to measure the frequency after the inter-RAT handover to the second base station is performed successfully; identifying that the inter-RAT handover is unnecessary based on the collected measurements results; and transmitting, to the first base station, a handover report indicating that the inter-RAT handover is unnecessary, the handover report including the identifier of the cell of the first base station.
 6. The method of claim 5, wherein the handover report further includes at least one of a handover type, a handover report type, a handover target ID, or a candidate cell list.
 7. The method of claim 5, wherein the identifier of the cell of the first base station includes an evolved-universal mobile telecommunication system terrestrial radio access network (E-UTRAN) cell global identifier (ECGI).
 8. The method of claim 5, wherein it is determined that the handover is unnecessary when the duration expires.
 9. A first base station in a wireless communication system, the first base station comprising: a transceiver configured to transmit and receive a signal; and a processor configured to control the transceiver to: transmit, to a second base station, a message requesting an inter-radio access technology (RAT) handover from a cell of the first base station to a cell of the second base station, the message including inter-RAT measurement configuration information, a tracking area identity (TAI), an identifier of the first base station, and an identifier of the cell of the first base station, and receive, from the second base station, a handover report indicating that the inter-RAT handover is unnecessary after the inter-RAT handover to the second base station is performed successfully, the handover report including the identifier of the cell of the first base station, wherein the inter-RAT measurement configuration information includes information on a duration in which the second base station is to collect measurement results and information on a frequency for which the second base station collects the measurement results, and wherein the measurement results are received from the UE by instructing the UE to measure the frequency.
 10. The first base station of claim 9, wherein the handover report further includes at least one of a handover type, a handover report type, a handover target ID, or a candidate cell list.
 11. The first base station of claim 9, wherein the identifier of the cell of the first base station includes an evolved-universal mobile telecommunication system terrestrial radio access network (E-UTRAN) cell global identifier (ECGI).
 12. The first base station of claim 9, wherein it is determined that the handover is unnecessary when the duration expires.
 13. A second base station in a wireless communication system, the second base station comprising: a transceiver configured to transmit and receive a signal; and a processor configured to: control the transceiver to receive, from a first base station, a message requesting an inter-radio access technology (RAT) handover from a cell of the first base station to a cell of the second base station, the message including inter-RAT measurement configuration information, a tracking area identity (TAI), an identifier of the first base station, and an identifier of the cell of the first base station, the inter-RAT measurement configuration information includes information on a duration in which the second base station is to collect measurement results and information on a frequency for which the second base station collects the measurement results, control the transceiver to receive measurements results of the frequency for the duration of collecting the measurements results by instructing the UE to measure the frequency after the inter-RAT handover to the second base station is performed successfully, identify that the inter-RAT handover is unnecessary based on the measurements results, and control the transceiver to transmit, to the first base station, a handover report indicating that the inter-RAT handover is unnecessary, the handover report including the identifier of the cell of the first base station.
 14. The second base station of claim 13, wherein the handover report further includes at least one of a handover type, a handover report type, a handover target ID, or a candidate cell list.
 15. The second base station of claim 13, wherein the identifier of the cell of the first base station includes an evolved-universal mobile telecommunication system terrestrial radio access network (E-UTRAN) cell global identifier (ECGI).
 16. The second base station of claim 13, wherein it is determined that the handover is unnecessary when the duration expires. 